Remove mentioning of removed example from progressbar docs (#8799)

* Remove mentioning of removed example from progressbar docs

documentation/components/components-progressbar.asciidoc

 <<dummy/../../../framework/advanced/advanced-push#advanced.push,"Server Push">>
 for instructions about using server push. Whichever method you use to update the
 UI, it is important to lock the user session by modifying the progress bar value
-inside [methodname]#access()# call, as illustrated in the following example and
-described in
+inside [methodname]#access()# call, as described in
 <<dummy/../../../framework/advanced/advanced-push#advanced.push.running,"Accessing UI from Another Thread">>.
 
 [source, java]